1. Field of the Invention
The present invention relates to microscale and nanoscale arrays of electrochemical cells and batteries for computer and nanodevice memory and power supply. Specifically, the present invention relates to a two-dimensional array of electrochemical cells or batteries that may be used to store both digital and analog information. Techniques for both read-only and read-and-write memory storage are disclosed.
2. Prior Art
Nanotechnology is a rapidly expanding field. The desire for miniaturization of electronics, assays and memory devices stems from many factors. Smaller devices require less material, thereby reducing production costs. Because the distances between points are shorter, nanoscale circuitry operates much more quickly than larger circuit boards. Information stored in very small devices may be accessed and read very rapidly. Smaller devices are also less cumbersome and more easily transported.
The extremely high speed and small volume of microscale and nanoscale memory devices make then highly desirable. This has led to research into a variety of methods to form extremely small memory storage devices.
Atomic force microscopy (“AFM”) cantilever tips have become a common tool in nanotechnology. AFM tips were originally developed in order to study surface topography of a material at the molecular level. Changes in the surface of as little as a few tenths of nanometers (Angstroms) may be discerned utilizing AFM tips. When an electric current is applied to an AFM tip may also be used for scanning tunneling microscopy (“STM”). This also provides for nanometer scale readings of a surface's topography.
AFM tips have found a variety of other uses. They may by used to move individual atoms about a surface to create a variety of structures on the atomic level. AFM tips have been used to puncture holes into a surface. For example, W. P. King, T. W. Kenny, K. E. Goodson, G. C. M. Despont, U. Durig, H. Rothuizen, G. K. Binnig, P. Vettiger, Applied Physics Letters, 78, 1300 (2001); E. Gorchowski and R. F. Hoyt, IEEE Trans. Magn., 32, 1850 (1996); D. A. Thompson and J. S. Best, IBM J. Res. Dev., 44, 311 (2000)). The surface has a thin layer of a material having a relatively low melting point. An AFM tip is heated to a temperature above the surface's melting point and is then applied to the surface. The tip melts a cavity into the surface. This device is used to store data in binary code. When a non-heated tip is run across a series of cavities, the presence of a cavity may serve as a “1” while portions of the material that are not punctured serve as a “0”. One disadvantage of the IBM technique is that it is difficult and time consuming to effectively remove a single data point. Another disadvantage is that it is difficult to effectively erase stored data completely. The more data that is stored and erased on a surface, the more convoluted the surface becomes and eventually no longer performs adequately. Another disadvantage is that this technique may only store digital, binary data.
Another emerging tool in Nanotechnology is the use of crossbar switches. Crossbar switches form an array of switches by arranging a two-dimensional array of wires in an x-y format. Each switch is formed by connecting one set of parallel wires to every wire of a second set of parallel wires, wherein the second set of wires intersects the first set. Typically, the two sets of wires are perpendicular to each other, but this may not always be the case. A crossbar system is a superior way of accessing nanobatteries since 2n nanowires in the crossbar system can be accessed by n larger (micro size) wires using a demultiplexer circuit. This allows excellent scaling between the microscale and nanoscale world. For example, Hewlett-Packard Company (“HP”) has developed a demultiplexer for a molecular wire crossbar network in U.S. Pat. No. 6,256,767. HP's device comprises a two-dimensional array of nanoscale switches, each switch comprising a pair of crossed wires which form a junction where one wires crosses another and at least one connector species connecting said pair of crossed wires in said junction. The HP patent contemplates the connector species being a bi-stable molecule capable of having two local energy states. A disadvantage of HP's device is that the bi-stable molecule is only capable of two energy states. One of the advantages of the present invention using electrochemical cells or batteries as the “connector species” is that the system measures potential and/or charge of individual electrochemical cells, which may also be utilized to store and read analog data. This is because both charge and potential of the electrochemical cells will decrease over time. The change in potential or charge over time follows a measurable rate of decay.
The crossbar system of the present invention is a superior way of accessing nanobatteries for memory arrays and for power that might be needed from the nanobatteries. Ordered arrays of nanobatteries having electrodes result in memory systems of expanded capacity. The current magnetic data storage capacity is eventually expected to reach a limit of 100 Gb/in2. An electronic crossbar system for accessing arrays of nanobatteries for mass memory storage has the potential of obtaining a data density as high as 400 Gb/in2, which means the system contemplated under the present application has vast advantages over current magnetic memory systems. Further, the use of the present invention's nanobattery arrays on nanodevices such as microelectrical mechanical systems (“MEMS”) and nanoelectromechanical systems (“NEMS”) is very unique in that they can serve as both power sources and memory elements, saving space and resulting in further reduction in size of these devices.
Nanoscale batteries have also been of interest as means for supplying system power to nanoscale devices. Thin-film rechargeable batteries with active layers of 1-10 μm have been of interest since the 1980's, and previous studies have dealt almost exclusively with thin film work (See, for example: J. B. Bates, G. R. Gruzalski, M. J. Dudney, C. F. Lick, H.-h. Yu, and s. D. Jones, Solid State Technology, 36, no 7, 59, 1993). Thin-film microbatteries have been made by a deposition technique using a metallic lithium electrode layer with a solid Li3PO4 electrolyte. However, these batteries have lateral dimensions greater than a centimeter and produce current densities of only 8.3 μA/cm2 at an output voltage of approximately 4 V. A microbattery using a Ni/Zn electrode couple with an aqueous KOH electrolyte has also been developed (see, for example: L. G. Salmon, R. A. Barksdale, B. R. Beachem, R. M. LaFollete, J. N. Harb, J. d. Holladay, and P. H. Humble, “Development of Recharge Microbatteries for Autonomous MEMS Applications,” Solid-State Sensor and Actuator Workshop (Transducer Research Foundation, Inc. Hilton Head, S.C. 1998) pp 338-341). Once again, fabrication involves a deposition process for the two electrodes, with a polymer layer that is later removed to form the electrolyte cavity. These planar microbatteries were 200 μm×200 μm and had capacities of 200-200 mC/cm2 at current densities of 10-20 mA/cm2 with an operating voltage of 1.5 V. A carbon-based rechargeable lithium microbattery has been contemplated, but the progress in fabricating the electrode microstructure has been slow. This technology is based on photoresist technology commonly used in the semiconductor industry and electrodes are to be made from arrays of microelectrodes having diameters as small as 5 μm (See, for example: Kinoshita, K., Song, X., Kim, J., Inaba, M., Kim, J., Journal of Power Sources, 82, 170, 1999). The majority of the most recent papers on microbatteries follow these trends by describing systems where very thin films of electrolyte material were used to construct the battery, or by discussing the potential for these films to be used in batteries. The actual size of the batteries based on these electrodes structure is much greater than the nanometer scale. (Levasseur, A., Vinatier, P., Gonbeau, D., Bull. Mater. Sci., 22 (3), 607 (1999); Han, K. S. Tsurimoto, S., Yoshimura, M., Solid State Ionics, 121 (1-4), 229 (1999); Park, Y., Kim, J. G., Kim, M. K., Chung, H. T., Um, W. S., Kim, M. H., Kim, H. G., J. Power Sources, 76 (1), 41 (1998); N. C. Li., C. J. Patrissi, G. G. Che, and C. R. Martin, J. Electrochem. Soc., 147, 2004 (2000); N. C. Li, C. R. Martin, and B. Scrosati, Electrochem. and Solid State Lett., 3, 316 (2000)).
Additional attempts have been made to fabricate micro and nanobattery components and systems taking advantage of nanoscale technology and assembly. Nanoscale electrode systems have been made using a template synthesis method. Systems composed of LiMn2O4, SnO2, TiS2, sol-gel V2O5 materials, and carbon tubes have been used to make nanoscale electrode materials that typically show higher capacities, lower resistance, and lower susceptibility to slow electron-transfer kinetics than standard electrode configurations (V. M. Cepad, J. C. Hulteen, G. Che, K. B. Jirage, B. B. Lakshmi, E. R. Fisher, and C. R. Martin, Chem. Mater. 9, 1065 (1997); C. J. Patrissi and C. R. Martin, 146, 3176 (1999); G. G. Che, B. B. Laksmi, E. R. Fisher, and C. R. Martin, Nature 393, 346 (1998); S. V. Batty, T. Richardson, F. B. Dias, J. P. Voss, P. V. Wright, and G. Ungar, Thin Solid Films, 284-285, 530 (1996); Y. Zheng, F. B. Dias, P. V. Wright, G. Ungar, D. Bhatt, S. V. Batty, and T. Richardson, Electrochem. Acta, 43, 1633 (1998)). Langmuir-Blodgett films have been made with ion-conducting layer that have the potential to be used as electrolytes in nanobattery systems. Self-assembly mechanisms may also be used to construct high energy density, rechargeable lithium ion batteries by using a layer-by-layer self-assembly of poly(diallyldimethyl-ammonium chloride), graphite oxide nanoplatelets and polyethylene oxide on indium tin oxide with a lithium wire as a counter electrode. Systems with ten (10) self-assembled layers have high specific capacities ranging from 1100 to 1200 mAH/g. (J. H. Fendler, J. Dispersion. Sci. Tech., 20, 13 (1999).
Assignee is the owner of U.S. Pat. No. 6,586,133 for “Nano-Battery Systems,” which is incorporated herein by reference, and which discloses a process of providing a membrane with a plurality of pores, filling the membrane pores with an electrolyte, and capping the filled pores with electrodes.
The use of AFM tips and crossbar systems for fabrication and data storage has evolved separately from the techniques being developed for making nanoscale batteries. Nothing in the prior art has contemplated the use of arrays of miniaturized batteries to store data at a very small scale.
It is therefore desirable to develop a nanoscale storage device that may be erased and rewritten several times without deteriorating.
It is desirable to develop a nanoscale memory device capable of storing analog information.
It is also desirable to provide a nanoscale memory device that uses an electronic charge or current to store both erasable and permanent information.